Plasma or dry etching is a well known technique used in the fabrication of integrated circuits wherein gas which has been dissociated into positive and negative ions and radicals react with unprotected areas of a material disposed on a substrate to remove elected portions of the material from the substrate. The etching generally takes place in a chamber containing the etching gas, which is formed into a plasma by the application of R.F. frequency power in a relatively low pressure environment.
Another etching technique often used in conjunction with the above technique is known as downstream etching. In this technique the plasma is created outside the main etching chamber in an auxiliary chamber with the reactive species being transported to the main chamber where the etching takes place. Downstream etching is a specialized form of etching and is used, e.g., to strip the remaining photoresist from the substrate as well as to remove materials such as polycrystalline silicon and silicon nitride. The foregoing etching is often used as a clean-up operation after the main etching has been accomplished.
A typical method for creating the plasma is to pass the etching gas through a tube with a portion thereof subjected to an electric discharge. Discharge in the flowing etching gas can be created at various frequencies with or without electrodes. Discharges employing electrodes suffer from the erosion of the electrodes which creates dust that adheres to the wafer. Electrodeless discharges attempted heretofore required devices to couple the energy into the discharge, which were expensive and required adjustment between starting and maintaining the discharge.
It is, therefore, an object of the present invention to create a new and improved device which creates an electrodeless discharge and which is self starting and requires no coupling device.
This and other advantages of the device of the invention compared to devices heretofore utilized for the above-stated purposes will become apparent as the discussion proceeds.